Today we're making available the release candidate (RC) of Windows Vista SP1 via Microsoft Connect, and tomorrow subscribers to TechNet and MDSN will have access to those RC bits too. In addition, the RC will be available to the public next week via Microsoft's Download Center. The release candidate phase of beta software is typically the final phase before the RTM (release-to-manufacturing) of a product and indicates that the code has attained a significant level of performance and stability.

Let me call out several changes made since the Beta release of Service Pack 1 -- many of which came about as a result of direct feedback from our Beta-testing community (thank you!):

The size of the standalone installers have decreased significantly. For example, the standalone installer packages consisting of all 36 languages (x86 and x64 chip architectures) are smaller by over 50%. The standalone installer packages consisting of just the 5 languages (again, x86 and x64) slated for initial release are more than 30% smaller in size.

The required amount of disc space for SP1 installation has also decreased significantly. Furthermore, with the RC, if more space is required to install SP1, an error message will now display exactly how much space is needed to complete the installation.

Previous SP1 versions left behind a directory of files that wasn't needed after installation and occupied about 1GB of space; the RC includes automatic disk clean-up to remove this directory.

Installation reliability has been improved based on bug reports and error codes reported from Windows Update (thanks, Beta testers!). Testing shows that these improvements have significantly increased the proportion of successful installations of the RC.

We've improved the user experience of installing SP1 via Windows Update. During the Beta release, users installed without much guidance from Windows Update. The RC now contains a series of screens with detailed information on SP1.